The present disclosure relates to a method for dispensing solid compound pastes for surface treatment to a machining tool. The disclosure further relates to a device for dispensing solid compound pastes for surface treatment to a machining tool. More generally, the disclosure relates to improvements in methods for machining workpieces with solid compound pastes for surface treatment, and to improvements in automated machining (surface processing) of workpieces. In some exemplary embodiments, the disclosure further relates to a use of a solid compound paste for surface treatment.
German utility model DE 298 23 896 U1 discloses a paste dispenser, particularly for melting and applying a free-flowing, meltable medium that is composed of a storage funnel, a pressure cylinder, a conveyor cylinder, a heatable pressing-out chamber and a pressing-out nozzle.
The present disclosure generally relates to the field of surface treatment, particularly to the field of mechanical surface treatment. The term surface treatment may particularly be understood as involving polishing processes, brushing processes, grinding processes and similar material removing and/or surface-flattening processes. Whenever in the context of the following observations polishing machines, polishing disks, polishing pastes and similar terms are used, this shall generally also involve the corresponding equivalent from grinding machining, shipping machining and/or brushing machining. There is often a floating transition from polishing machining to grinding machining. Polishing applications are frequently assigned to the field of mechanical fine machining, particularly to the field of mechanical ultra-fine machining of surfaces.
Polishing, brushing and grinding may generally be referred to as subgroups of smoothening machining processes. Brushing applications, polishing applications and grinding applications may partially overlap one another. Polishing is generally based on different operating principles. On the one hand, a certain removal of material is present in polishing. Further, polishing regularly results in a deformation and particularly a levelling of roughness peaks of a surface structure of the workpiece. Polishing may further involve at least partially filling up cavities and/or irregularities. Generally, polishing methods, brushing methods and grinding methods are used to reduce the surface roughness of parts and, in some applications, to generate a shine on the surface of the part. Further applications are conceivable wherein the main focus is on burr removal and such like.
Common devices for polishing generally involve at least one polishing disk and/or a polishing belt. The polishing disk may provide a carrier material that is manufactured from natural material (natural fibers, cotton, sisal, paper, etc.) or from artificial material (artificial fibers). Also sponge-like materials may be used for polishing disks. Generally, polishing machining is performed by applying an appropriate polishing agent to the polishing disk. Due to a relative movement between the polishing disk and the workpiece to be machined, the respective polishing agent may contact the workpiece to act thereon in a processing, particularly smoothening manner.
Polishing disks, brushes or grinding discs may comprise operating regions that involve fabrics in general, cotton, sisal, polymers, paper, felt, leather and similar components. The disks may generally be referred to as polishing agent carrier. The abrasive grain may be formed, for example, on the basis of alumina, aluminum oxide, chromium trioxide or similar hard materials.
The present disclosure further relates particularly to the field of industrial grinding and/or polishing, and in some respect to highly automated grinding and/or polishing. Grinding devices or polishing devices are known that involve machining cells, for instance, wherein, on the one hand, the polishing device as such and, on the other hand, also elements for automated feeding of workpieces to be machined are present. By way of example, handling devices such as robots, rotary transfer machines or flatbed polishing machines may be provided are arranged to grip workpieces to be machined and to bring the same into contact with the polishing disk. Further, the handling devices may be arranged to effect a relative movement between the workpiece and the polishing disk to machine the desired regions of the workpiece. In other words, and handling robot may be provided, for instance, that imitates a “manual” swiveling and/or displacing of the workpiece relative to the (rotating) polishing disk.
It is generally necessary to replace the dissipating polishing agent at the polishing disk. This is often performed at intervals and/or quasi-continuously. By way of example, the polishing agent may be “massaged” in the polishing disk. The application of massaging in may be performed intermittently and/or periodically. Commonly, agents that are at least partially effective for abrasive purposes, more generally, agents for surface treatment, i.e. for instance polishing agents, brushing agents or grinding agents, are offered in defined dosage forms and/or states. This may involve, for instance, solid compound pastes or emulsions. Further, polishing agents and such like may be present in a form of ointments, creams and/or polishes.
Emulsions for surface treatment are commonly composed of a mixture of water, fats, oils and abrasive grain (commonly based on ceramics) that is ideally uniformly distributed in the emulsion. Emulsions for surface treatment are commonly liquid and pourable at room temperature (25° C.). A consistency is comparable, for instance, with a consistency of drinkable yoghurt. As the respective emulsions are pourable already at room temperature, the emulsions may be simply conveyed via piping systems, tubes and such like. The emulsions may be applied through spraying nozzles and sprayed on the polishing tool.
Solid compound pastes for surface machining form a second substantial group of grinding agents or polishing agents. Solid compound pastes generally involve mixtures of lipids (comprising for instance fats, oils and waxes), additives admixed thereto, and a respective share of abrasive grain that is admixed to the carrier material, ideally uniformly dispensed. Depending on the intended application, the abrasive grains may involve a size of 0.1 μm (micrometer) to about 200 μm. The abrasive grains may form a mass fraction of 50% to 80% of the paste. Generally, solid compound pastes are mixed and/or formulated at a slightly increased temperature. A mixture that is formed in this way is generally poured in molds to be present, after solidifying, as bar-shaped or rod-shaped solid compound pastes. Rods of solid compound pastes that are suitable for industrial machining may have a length of about 300 mm to 500 mm. In particular, solid compound pastes of this kind may be referred to as so-called automat bars. Solid compound pastes may involve polishing pastes, brushing pastes, grinding pastes and appropriate mixtures thereof.
Solid compound pastes feeding apparatuses are known into which rods of this kind may be clamped. Feeding apparatuses of this kind may involve drives that enable a feeding movement having a pilger process character. By way of example, the rod may be pushed against the rotating grinding or polishing disk at regular (temporal) intervals. Due to the relative movement between the disc and the solid compound paste, significant friction heat is generated by means of which the solid compound paste is softened and/or melted at its contact surface with the disc. Accordingly a certain part of the softened material is transferred to the polishing tool. Due to the huge circumferential velocity of the discs, this kind of transfer often involves losses. Parts of the melted and/or softened solid compound paste are simply thrown away from the disc. It may be commonly expected that 50% to 80% of the solid compound paste are received by the disc and usable for machining purposes. The remaining fraction (20% to 50%) may not be used for the machining process and have to be accepted as losses.
Both the machining with solid compound paste bars and the machining with emulsions involve several drawbacks. Polishing with solid compound pastes and particularly solid compound paste feeding apparatuses for the automated machining are essentially based on traditional and tried and tested technologies. Solid compound paste feeding apparatuses “imitate” a manual application of the polishing agent to the polishing disc. The maximum length of the rods, however, limits the possible operating time of such a polishing device as accordingly new rods have to be reloaded when an older rod is consumed. This stands in contrast to the concept of automated machining.
Further, a solid compound paste rod often may not be entirely processed as a minimum length may not be undercut. This may be required, on the one hand, due to safety aspects (refer for instance to a minimum pad thickness of a brake pad). Further, this may be simply caused by the fact that the rod has to be guided and gripped in the solid compound paste feeding apparatus to provide a feed that is for instance pilger process like. The mentioned residual amount therefore even further increases the losses. It is also adverse from an environmental perspective and from a disposal perspective that—depending on the actual application conditions—no more than half of the basically provided paste amount is actually usable for machining. When transferring the paste to the polishing disc partial amounts of the paste are regularly thrown away. Accordingly, a great mess may be present. Solid compound paste feeding apparatuses always have to be placed in close proximity of the polishing disc and/or the polishing wheel to be able to bring the rod into engagement with the wheel, respectively. Hence, solid compound paste feeding apparatuses are strongly exposed to the contamination.
A further drawback of established methods for machining with solid compound paste bars can be seen in the requirement that the solid compound paste bar and/or the solid compound paste rod ideally comprises a width that is adapted to the width of the polishing disc. This results in a huge variety of variance and increases the unit costs.
The emulsions for surface treatment described further above, however, may basically be processed in an automated fashion as they are flowable (fluid) already at room temperature. However, it has been observed that the grinding result and/or polishing result when using solid compound pastes is often superior to the result when emulsions are used. Further, with solid compound pastes, often shorter cycle times are possible. Emulsions are always formulated under the condition of the required ability to flow and/or to be pumped at room temperature. Accordingly, the composition of an emulsion may be varied only in relatively narrow borders. In contrast thereto, solid compound pastes enable significantly further reaching variations and modifications in terms of their composition.
Also with polishing methods that involve polishing agents in the form of emulsions, a considerable amount of the emulsion may get lost without being usable for the machining. This is explainable with the slinging way of partial amounts of the emulsions due to the polishing discs rotating at huge circumferential velocity.
Further, it could be observed in some cases that grinding and polishing waste based on polishing agents or grinding agents sometimes have a tendency to self-heating and/or self-ignition. This may involve, as the case may be, even the initiation of fires and, accordingly, involve a huge risk for the manufacturing facilities and also for operating staff.
Further, polishing agents on the basis of solid compound pastes are superior over emulsions as considerably fewer conditions have to be complied with for storing the same. In particular, it could be observed that emulsions (dispersions) may undergo self-demixing at low temperature (for instance under 0° C.) and at temperatures higher than about 40° C. This may involve that the emulsions become unusable and simply have to be disposed, at worst case as special waste. Also in terms of time, relatively in narrow limits must be observed with when storing emulsions. Solid compound pastes are significantly less sensible in terms of temperature variations and extreme temperature. Commonly, polishing agents on the basis of solid compound pastes may be moved and/or stored at between about −60° C. to +80° C. Increased temperature may in fact involve deformations when fractions of the solid compound paste are melted. However, this is generally a reversible process and does not have an adverse effect on the suitability for use of the solid compound pastes.
The afore-mentioned DE 298 23 896 U1 generally proposes, in fact, to use a free-flowing and meltable polishing agent to combine based thereon the advantages of solid compound pastes and emulsions (referred to as liquid pastes in DE 298 23 896 U1). It is generally stated to this end to implement a pressure cylinder, a conveyor cylinder, a heatable press-out chamber and a press-out nozzle. However, in no way details of such an arrangement are mentioned in DE 298 23 896 U1. If at all, it may be concluded from this document that apparently free-flowing pastes are conveyed by means of a conveyor system towards the heatable press-out chamber and the press-out nozzle. Apart from that, no hints or suggestions of how to arrange such an apparatus and of how to render it operative are present in this document. Further, no further reference to the polishing agents used can be found in the document.
In view of this, it is an object of the present disclosure to present a method for dispensing solid compound pastes for surface processing that may be used with automated machining facilities for grinding machining and/or polishing machining and that may further increase the degree of automation thereof, at least in some embodiments.
It is a further object of the present disclosure to present a corresponding device for dispensing solid compound pastes for surface processing.
It is a further object of the present disclosure to present improvements in surface processing methods and devices that facilitate the use of polishing agents on the basis of solid compound pastes in manufacturing facilities for surface processing, involving polishing and grinding processing.
It is a further object of the present disclosure to present improvements in surface processing methods and devices that enable a continuous or quasi-continuous supply with the solid compound paste, preferably without the need of replacing polishing bars, polishing rods and similar partial amounts of the solid compound paste at a high replacement frequency.
It is a further object of the present disclosure to present improvements in surface processing methods and devices that enable a minimization of losses when applying or transferring the solid compound paste to the polishing disc or the polishing belt.
It is a further object of the present disclosure to present improvements in surface processing methods and devices that enable cost savings preferably by increasing the operating time available for processing and by reducing idle times and polishing paste losses.
It is a further object of the present disclosure to present a method for surface treatment of workpieces and a corresponding system that is suitable for performing the method, wherein both the method and the system may profit from the supplying/dispensing method and device described herein.
It is a further object of the present disclosure to present potential uses of a polishing agent in the form of solid compound pastes in a method for dispensing solid compound pastes and/or for surface treatment using solid compound pastes.